(1) Field of the Invention
The present invention relates to a scheduling method and program for a substrate processing apparatus that performs predetermined processes on semiconductor wafers or glass substrates for liquid crystal displays (which will be referred to hereinafter simply as substrates).
(2) Description of the Related Art
A conventional scheduling method for such a substrate processing apparatus may be the event drive type that performs one process after another.
One lot of substrates is processed according to a predetermined recipe as shown in the table of FIG. 1, which includes seven processing steps “a” to “e”, for example.
With this recipe, the processing steps are executed in the order of a, b, c, b, d, b and e. Each processing step in this example is divided into three operations of “preliminary operation”, “main operation” and “subsequent operation”. The numerals in the table of FIG. 1 exemplify processing times (minutes) of the operations in the processing steps “a” to “e”. Broadly, what is done in each processing step is as follows, for example. The processing step “a” is to take substrates out of a cassette and prepare the substrates for transportation. The processing step “b” is to transport the substrates. The processing step “c” is to apply a chemical to the substrates and clean the substrates with deionized water. The processing step “d” is to dry the substrates. The processing step “e” is to transport the substrates and deposit the substrates in a cassette.
The table of FIG. 1 purports the following particulars also.
The processing step “a” completes a preliminary operation in one minute, then processes one lot of substrates in a main operation which takes five minutes, and performs a one-minute subsequent operation. The processing step “b” completes a preliminary operation in one minute, and processes the one lot of substrates in a main operation which takes four minutes, with no subsequent operation. The processing step “c” completes a preliminary operation in two minutes, then processes the one lot of substrates in a main operation which takes five minutes, and performs a one-minute subsequent operation. The processing step “b” executed a second time performs a one-minute preliminary operation and a three-minute main operation. The processing step “d” performs a two-minute preliminary operation, a three-minute main operation and a one-minute subsequent operation. The processing step “b” executed a third time performs a one-minute preliminary operation and a four-minute main operation. The processing step “e” performs a two-minute preliminary operation and a six-minute main operation.
FIG. 2 shows a time chart of the processes performed on one lot of substrates according to the recipe shown in FIG. 1.
Upon completion of the main operation in the processing step “a”, a completion signal “e” is outputted (as indicated by an ordinary arrow) to a processing unit that executes the next processing step “b”. Only at this point of time does the processing unit start the preliminary operation in the processing step “b”. The substrates are actually transferred to the processing step “b” at a point of time referenced “m” (indicated by a black triangular arrow). Similarly, after a completion signal “e”, the lot is actually transferred to each subsequent processing step at a point of time “m”.
FIG. 3 shows a time chart of a successive processing of two lots by the above event drive type. In FIG. 3, the white rectangles represent the first lot, and the hatched rectangles the second lot. Thus, completion of the main operation in each processing step is notified to the next processing step, whereupon a preliminary operation is started, and substrates are actually transferred when the preliminary operation is completed.
The conventional practice noted above has the following drawback.
According to the conventional scheduling method noted above, upon completion of a main operation, the completion is notified to a next processing step, and then a preliminary operation in the next processing step is started. Since the processing is performed in this way, numerous standby periods (black portions) occur as shown in the time chart of FIG. 3. Thus, each processing unit of the substrate processing apparatus has markedly low time efficiency.
Where the substrate processing apparatus includes a chemical processing unit using a processing or treating solution, the treating solution must be changed regularly according to the life of the treating solution, i.e. “lifetime” based on use time of the treating solution and “life count” based on use frequency of the treating solution.
In the conventional substrate processing apparatus, therefore, transport of a new lot from a loading section is stopped on information that the life count or lifetime is up. Then, when no lot remains to be processed in the chemical processing unit, an operation is carried out to change the treating solution.
This conventional practice has the following drawback.
When a lot is present in the conventional substrate processing apparatus and the recipe requires use of the chemical processing unit, a processing has to be continued until this lot is processed even though the treating solution is depleted. In other words, priority is afforded to the processing of a lot, which tends to delay changing of the treating solution. This brings about a failure to change the solution according to the lifetime or life count.
The above failure in timely changing of the solution results in a processing with the depleted treating solution. This could lower repeatability of the processing or cause a defective processing.